Pumping and servicing rig

ABSTRACT

An improved pumping rig for an oil well or the like having a 2 to 1 hydraulic powered lift assembly counterbalanced by a separate circuited hydropneumatic cushioning system and a reciprocatory movement control system using a third separate hydraulic circuit. The crown assembly includes a sheave and strap arrangement in place of unsatisfactory chains and sprockets. An internal safety bleed system is provided in the drive cylinder to create an hydraulic lock in the event of piston overtravel due to rod string failure or other malfunction. The hydropneumatic cushioning system includes vertical cylinders in fluid communication with air-hydraulic fluid surge tanks having slotted, anti-slosh tubes therein.

United States Patent [1 1 Bender Dec. 11, 1973 PUMPING AND SERVICING RIG [76] Inventor: Emil A. Bender, 6625 Kane Way, 5 a qif' jf Gwlghegan Bakersfield, Calif. 93309 [22] Filed: July 24, 1972 [57} ABSTRACT [21] App]. No.: 274,248 An improved pumping rig for an oil well or the like having a 2 to l hydraulic powered lift assembly counterbalanced by a separate circuited hydropneumatic [g2] 60/37F21,56b0/13/3 cushioning System and a reciprocatory movement com d 51 372 trol system using a third separate hydraulic circuit. 1 0 care 6 The crown assembly includes a sheave and strap arrangement in place of unsatisfactory chains and sprockets. An internal safety bleed system is provided [56] References cued in the drive cylinder to create an hydraulic lock in the UNITED STATES PATENTS event of piston overtravel due to rod string failure or 2,564,285 8/1951 Smith 60/52 PJ X other malfunction. The hydropneumatic cushioning 2,617,256 11 /1952 White 60/52 PJ X system includes vertical cylinders in fluid communica 2,645,399 7/ 1953 at 60/52 P] X tion with air-hydraulic fluid surge tanks having slotted, 2,768,500 10/1956 Tyler 60/52 R amides}, tubes therein 2,807,935 10/1957 Lapsley 60/19 2,887,846 5/1959 Habenicht 60/52 F] X 10 Claims, 21 Drawing Figures I I W I e i "l 1 1 1 1 1 I I I 1 ,1

PAIENIEUBEEI 1 I915 sum 2 or 5 FIG. 3

PUMPING AND SERVICING RIG BACKGROUND OF THE INVENTION Prior art oil well pumping rigs of the long stroke variety require complex prime mover systems together with unsatisfactory counterbalance weights and associated lift chains, sprockets and other mechanical items all subject to wear and failure in an unacceptably short period of time. Furthermore, for safety of operation, such prior units require expensive, multiple safety devices and each mechanical part of the overall rig thereby creating excessive cost of manufacture.

Required equipment for extracting oil over the entire productive life of an oil well may vary considerably. Specifically, during the so-called early life of an oil well, reservoir pressure alone may be sufficient for recovery of the oil providing the local regulatory authority sanctions such a technique. More commonly, and in any case eventually, a pump must be used to recover the oil. A most common variety of pump is the walking beam pump utilizing a reciprocating sucker rod suspended from the surface by a rod string. Such units have a nominal stroke distance of from 7 to about 12 feet or a little more.

However, as the search for oil widens to more remote areas of the world and to greater depths, such pumps become progressively less efficient and eventually are completely useless. For example, where the depth of the well approaches 5,000; 8,000 and 12,000 feet or even more, the stretch of the rod string on the upstroke will be on the order of several feet or more, which must be deducted from the stroke distance of the walking beam pump to determine the effective pump stroke. Obviously, this value approaches zero with deeper wells.

This situation has led to the development of long stroke oil well pumps, having a stroke distance of generally 32 feet or more so that oil may be efficiently pumped from deep wells even though several feet of stroke distance is lost through rod stretch. Rigs have been developed comprising a central derrick or tower having a crown block assembly suspending the rod string on one side and a counterweight on the other to reduce power requirements and wear on the prime mover. The counterweight is effective during downstroke of the pump so that power required from the prime mover is substantially equalized throughout a reciprocatory cycle. One example of such a prior art longstroke pumping unit is the Oilwell Model 3534 Long Stroke Pumping Unit, manufactured by Oilwell, a division of United States Steel. The rig is described and illustrated in Oilwells Bulletin No. LS1869. Generally, this unit includes a central supporting tower having multiple guys to stabilize the structure, a complex muIti-strand cable crown block assembly suspending the rod string and a variable capacity counterweight, a prime mover, and several safety systems including an automatic air brake system controlled by an overspeed governor flyweight.

Improved long stroke counterbalanced pumps are disclosed in my prior U.S. Pat. No. 3,248,958, disclosing a wire line deep well pumping assembly; U.S. Pat. No. 3,345,950, where the above described counterweight suspension system was simplified to a pair of sprockets, constituting the crown block and chains over the sprockets interconnecting the rod string yoke and counterweight; U.S. Pat. No. 3,483,828, where the chains were made endless a similar unit is also disclosed in U.S. Pat. No. 3,515,008! to Davidescu et al.; and U.S. Pat. No. 3,538,777, where a belt strap and simple 2 to 1 ratio pulley system is disclosed providing a 32 foot effective rod string stroke for a 16 foot bydraulically powered piston stroke,

In addition to the disclosures of my above enumerated prior patents, the following twelve prior patents each disclose attempts to produce a satisfactory, maintenance free and simplified hydraulically actuated oil well pump. However, these have proven to be either too complicated and thus expensive for widespread use, or too small and otherwise unsatisfactory for deep well pumping.

U.S. Pat. No. 1,619,475 discloses an hydraulically actuated but short stroke oil well pump including a, fluid pressure counterbalance system acting directly beneath and coaxially with the power piston and cylinder lift pump apparatus via a common connecting rod to equalize drive force required from the same mover on both upstroke and downstroke of the pump. Safety bleeds are provided at each end of the power cylinder, but extra safety valve means must be provided to pre ventpiston overtravel in the event of oil well pump rod string failure. The same supply of hydraulic fluid is used for the power cylinder and for a four-way valve controlling reciprocation of the power piston. A separate fluid pressure supply is used for the counterbalance, but its character (liquid and/or gas and supply therefor) is not disclosed. U.S. Pat. No. 2,874,641 discloses a towerless, but extremely small, short stroke 2 to 1 ratio hydraulic oil well pump using lift chains and sprockets as the pulley system to interconnect the drive piston and rod, and the rod string. No counterbalance system is provided.

U.S. Pat. Nos. 2,504,218 and 2,572,748 disclose 2 to 1 ratio hydraulic oil well pumps having a gas-hydraulic fluid counterbalance, but the same fluid supply is employed for the pump and the counterbalance, and the piston-cylinder arrangement of the pump as well as the sprocket-chain construction of the 2 to 1 ratio connection, drive means to sucker rod string, make the unit highly impractical.'U.S. Pat. No. 2,520,187 discloses a similar pump but using a pure gas counterbalance sys tem. Other hydropneumatic counterbalance units are disclosed in U.S. Pat. No. 2,726,512 (deep well pumping unit) and Nos. 2,233,227; 2,233,245; 2,293,916; 2,432,735; 2,244,428; and 2,808,735 (walking beam pumps). A foam counterbalance unit is disclosed in U.S. Pat. No. 2,756,602.

While this array of prior art includes a wide variety of 2 to 1 ratio, counterbalanced hydraulic oil well pumps, it is important to note that no one or a combination of these disclosed prior art pumps have ever been found acceptable in an available commercial form.

In contradistinction to these prior art pumps, the present invention provides a greatly simplified 2 to 1 ratio counterbalanced hydraulic oil well pump having numerous individual improvements enhancing commercial marketability of such a pumping unit.

SUMMARY OF THE INVENTION Therefore, it is a primary object of the invention to provide a simplified, commercially acceptable and practical 2 to 1 ratio hydraulically actuated oil well pump and servicing rig.

It is another object of the invention to provide an hydraulic pump and servicing rig wherein three separate fluid systems are provided, one for the drive unit, another for the counterbalancing system, and a third for a control system governing reciprocation of the drive unit.

Yet another object of the invention is to provide a single simplified safety system for an hydraulic oil well pump and rig having no moving parts which assures complete shutdown of the system in the event of piston overtravel due to rod string failure or the like.

A further object of the invention is to provide an hydarulic oil well pump having a counterbalance system assuring smooth transition from a down stroke to an upstroke thereby minimizing the possibility of rod string failure. 1 l

A still further object of the invention is to provide an improved hydropneumatic counterbalance system for an hydaulically actuated oil well pump and servicing rig having primary, hydraulic fluid and air surge tanks and associated secondary air tanks manifolded to the primary tanks, the primary tanks having unique internal structure to minimize fluid slosh and the secondary tanks being provided to greatly reduce the pressure required in such counterbalance systems.

Another object of the invention is to provide a 2 to 1 ratio hydraulically actuated oil well pump and servicing rig employing a plain sheave and strap arrangement in place of the usual sprocket wheel and chain assembly interconnecting the rod string and drive unit.

Yet another object of the invention is to provide a counterbalanced hydraulically actuated oil well pump and servicing rig including counterbalancing cylinders each having a unique arrangement of guide rings, a drive cylinder having a piston with and excess fluid wiper ring, a dual strap and sheave interconnection from the drive unit to the rod string including polyethylene block supports for preventing relative strap slippage, and a novel dust seal and breather arrangement for the counterbalancing cylinders.

Further novel features and other objects of this invention will become apparent from the following detailed description, discussion and the appended claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS Preferred structural embodiments of this invention are disclosed in the accompanying drawings in which:

FIG. 1 is a top, plan view of the invention;

FIG. 2 is a side elevational view of the invention as shown in FIG. 1;

FIG. 3 is a partial front elevational view of the invention as shown in FIGS. 1 and 2;

FIG. 4 is a fragmentary side elevational view showing an alternative embodiment of the strap and sheave arrangement shown in FIGS. 1-3;

FIG. 5 is a partial front elevational view of the embodiment shown in FIG. 4;

FIG. 6 is a fragmentary front elevational view of yet another embodiment of the invention, depicting the dust seal and breather arrangement for one of the cylinders of the counterbalancing system;

FIG. 7 is a sectional view taken along lines 7-7 of FIG. 6;

FIG. 8 is a partial sectional view showing the interior details of the drive or power cylinder and piston of the invention;

FIG. 9 is a view similar to FIG. 8 but showing another embodiment of the drive cylinder;

FIG. 10 is a partial sectional view showing one cylinder and piston of the counterbalancing system;

FIG. 11 is a schematic diagram illustrating the primary, independent drive fluid circuit of the invention;

FIG. 12 is a fragmentary view taken from FIG. 11 showing valve reversal;

FIG. 13 is a partial top plan view showing the control system for reversing the valve shown in FIG. 12;

FIG. 14 is a partial side elevational view of the control system shown in FIG. 13;

FIGS. 15 and 16 are top plan and side elevational views respectively of the control valve schematically illustrated in FIG. 12; FIGS. 17 and 18 are top plan and side elevational views respectively of the valve element of the assembly shown in FIGS. 15 and 16;

FIGS. 19 and 20 are end elevational and partial top plan views respectively of the primary and secondary tank units forming part of the counterbalancing system; and

FIG. 21 is a partial sectional view of one of the primary, surge tanks shown in FIGS. 19 and 20, taken along lines 21-21 of FIG. 19 and drawn to an enlarged scale.

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the invention is shown in FIGS. 1, 2 and 3 having a skid base or platform 10 with power unit 12 and cushioned, hydraulically actuated pump 14 mounted thereon. Platform 10 is rather conventional in and of itself and includes a pair of outboard channel beams 16, 16 serving as orimary supports for the entire structure over a well head (not shown). The integral structure provided by beams 16, 16 permits ready positioning of the entire pump and servicing rig over a well head as well as easy portability of the unit from one well head to another. Beams 16, 16 may be mounted on a pair of L tracks (not shown) to further enhance portability of the invention. Suitable crossbeams are also provided (unnumbered) in conventional fashion to support power unit 12 and pump 14.

Since the primary use of the present invention is intended as an oil well pump, this term will be used hereinafter, although the invention could easily be used for oil well servicing and drilling as well. Thus, the use of the term pump to describe the invention is not intended to restrict use of the structure to that one limited function. DeLaval Turbine, Inc.

Power unit 12 (also schematically illustrated in FIG. 11) has a prime mover 18 preferably in the form of a diesel engine, although an electric motor could be employed if desired. Motor 18 transmits drive through a drive belt 20 to a standard torque converter 22 and hydraulic fluid pump 24. While pump 24 may be one selected from several hundred varieties currently available on the market, a preferred type is a constant displacement, rotary, screw type pump which has a minimum number of moving parts yet provides constant, uniform fluid flow. A preferred example of such a pump is the IMO pump produced by DeLavalTurbine, [No of Trenton, NJ. This axial feed pump has but one driven power rotor with two complementary idler rotors for feeding hydraulic fluid at pressures up to 3,000 psi in volumes from 1 to 4,000 gallons per minute. In any event, the specific internal characteristics of pump 24 form no part of the instant invention.

Fluid under pressure is driven from fluid pump 24 through a primary line 26 to a reversing valve 28 to reciprocate drive piston 30 in drive cylinder 32; exhausted fluid is returned through a line 34 and a oneway check valve 36 to a conventional fluid reservoir 38 which has a fluid line 40 therefrom, having another one-way check valve 42, for feeding fluid to the inlet sideof fluid pump 24. Motor 18 also drives a secondary drive belt 44 which in turn operates a small gas or air compressor 46 for supplying compressed air to the hydropneumatic cushioning system 48, which will be set forth in detail hereinbelow. Finally, motor 18 also drives a small hydraulic fluid pump (not shown) which provides fluid under pressure for a control system 50 (FIGS. 13 and 14) which governs reciprocatory movement of drive piston 30 in a manner set forth in detail hereinafter.

In a preferred embodiment, oil well pump unit 14 includes centrally disposed drive cylinder 32 and outboard cushion cylinders 52, 52 secured to either side thereof (FIG. 3) by suitable braces and framing means 54. It should be noted here that the construction of the instant invention completely negates the need for any derrick structure or guy wires, one of the mjaor deficiencies of the prior art. Such compact, derrick-less structure is also disclosed in one embodiment of the portable oil well servicing rig set forth in my prior copending US. Patent application Ser. No. 231,933 filed Mar. 6, 1972 and entitled SIMPLIFIED WELL RIG. If desired, the entire oil well pump unit 14 together with hydropneumatic cushioning system 48 and braces 54 may be pivotally mounted (not shown) for easier transport of the entire structure. Such pivoting would be to the left with reference to FIG. 2 with angle frame members 56 resting on supports 58 provided at the left hand side of platform 10.

In the embodiment shown in FIGS. 2 and 3, the upper end of drive cylinder piston rod 60 (see also FIG. 8) has a transverse cross brace 62 thereon integrally interconnecting the two piston rods 64, 64 of cushion cylinders 52, 52 (see also FIG. 10) and supporting axle 66 having rotatable sheaves 68, 68 at each distal end. Cushion cylinder piston rods 64, 64 may be square in cross section (FIGS. 2 and 3) or circular (FIG. 10) and suitable guide means such as rollers 70 (FIG. 3) may be provided to true the vertical reciprocation of rods 64, 64.

Rollers 70 are mounted on the uppermost cross brace of framing means 54.

A pair of loft strap assemblies 72, 72 are trained over sheaves 68, 68 each being fixed at its deadline end to anchor 74, mounted on platform 10, and at its working end to a yoke 76 which has a polished rod 78 secured centrally of yoke 76, the rod 78 being the upper end of a sucker rod string extending into the well (not shown) for lifting oil therefrom.

Thus it is seen that the simple sheave and strap assembly just described provides a two to one lift mechanism, in that for each reciprocatory stroke of rods 60, 64, 64, polished rod 78 will move twice the distance of movement of the rods. In a preferred embodiment, the stroke of rod 60 is eight feet and thus the effective stroke of polished rod 78 will be sixteen feet thereby providing a very suitable long stroke pumping unit.

FIG. 2 illustrates one novel and preferred lift strap assembly 72 used in the invention. Each strap is made of high tensile strength srping steel, such as cold rolled strip spring steel manufactured by Sandvike Steel, Inc. of Fair Lawn, N..l., each strap being 4 inches wide and 0.027 inch thick. The distal ends of each strap are secured through a polyethylene support block 80 which permits a slight amount of movement of each anchored end of the strap relative to the other. Such interplay assures retention of each strap assembly 72 on its respective sheave 68; since one strap is mounted on top of the other, each reciprocatory stroke of the pump will cause the upper strap to move a slight distance greater than the strap directly on sheave 68. Thus, polyethylene supports 80 impart transverse stabilization at the anchor ends and the lift ends of each strap assembly 72 regardless of the slight interplay between the straps. Although two straps are shown in the drawings for each strap assembly 72, one, or three or more straps might be used depending upon pump lift requirements.

A single lift strap arrangement is illustrated by FIGS. 4 and 5 wherein a single wide belt 82 is provided, trained over cylindrical rollers 84, 84 mounted forwardly and rearwardly of drive piston rod 60 on axles 86, 86. In this embodiment, the diameter of each roller (FIG. 4) may be smaller than the diameter of each sheave 68 (FIG. 2) and still suspend the polished rod out over the well head (not shown), away from the edge of platform 10, due to the front-to-rear arrangement of rollers 84, 84, rather than the side-to-side arrangement of sheaves 68, 68 in the preferred embodiment.

Yet another embodiment of lift straps and sheaves is illustrated in FIG. 6, wherein each sheave 68 is suspended beneath brace 62 on an independent axle 88. Also shown is a polyethylene impact block beneath each sheave 68 which will cushion the fall of the reciprocatory parts of the pump in the event of pressure failure in either the drive fluid circuit or the cushioning system or both thereby preventing any damage to the structure. Upon impact, block 90 may be distorted to the position shown in phantom lines in FIG. 6. Such blocks 90 may also be provided in the two previous embodiments described and shown in FIGS. 2-5, each being mounted on the top brace member of framing means 54, beneath cross brace 62 interconnecting rods 60, 64, 64 together.

The interior structures of drive cylinder 32 and cushion cylinders 52 are shown in cross section in FIGS. 8-l0. Drive cylinder 32, also schematically illustrated in FIG. 11, includes a double action piston 30, which reciprocates drive rod 60 to actuate the oil well pump as hereinbefore explained. Hydraulic fluid is fed into and bled from the lower side of piston 30 in conventional fashion, from line 92 communicating with revers ing valve 28 (FIG. 11). Fluid under pressure is fed to the top of drive piston 30 from reversing 28 through a line 94 and a manifold space 96 defined between outer cylinder jacket 98 and inner jacket 100 which constitute the drive cylinder 32. Fluid is directed interiorally of jacket 100 through an upwardly spiral arrangement of ports 102 which also serve as the primary, nonmoving parts safety mechanism for the invention. Specifically, in the event of piston overtravel upwardly, which might occur if the sucker rod string should fracture or fail, fluid under pressure beneath piston 30 will simply merely escape through ports 102 into manifold 96 and back to the fluid circuit. As the piston overtravels even farther, progressively more ports 102 are exposed to fluid under pressure from beneath piston 30 thereby decreasing and eventually negating any pressure beneath piston 30 altogether, thereby effectively stopping the pump. At the same tine, any possibility of damage to prime mover 18 or hydraulic motor 24 is completely eliminated, as ports 102 serve to completely short circuit fluid flow in the hydraulic fluid drive circuit thereby locking piston 30 in a state of overtravel while merely recirculating fluid through the drive fluid circuit without any undue strain being created on prime mover 18 or pump 24 as in the case of a true hydraulic lock condition. Furthermore, no safety release valves are required as in prior art systems, such valves not only tending to waste fluid but also being subject to failure themselves in that they require moving parts.

Rod 60 is sealed in more or less conventional fashion through top brace 54 by suitable packing means such as chevron seals 104 retained by packing ring 106, bolted to brace 54. Jackets 98 and 100 may be concentrically retained in place by a suitable spacer ring 108, above ports 102. If desired, suitable spacer blocks (not shown) might be inserted between jackets 98, 100, be neath ports 102. Of course, drive piston 30 also includes a suitable plurality of sealing piston rings 110.

Reference is now made to FIGS. 11 and 12 for an illustration of the relatively simple drive fluid circuit of the invention. In the configuration shown in FIG. 11, hydraulic fluid under pressure is being used to drive piston 30 downwardly, with fluid from pump 24 being fed through line 26, reversing valve 28 and line 94 through manifold 96 to the top of drive piston 30. Fluid beneath piston 30 is bled through line 92 and reversing valve 28 to return line 34 to storage tank 38, through the usual check valve 36 to prevent backfeed in the system, and to the inlet port of pump 24 from storage tank 38 through line 40 and a second one-way check valve 42.

Control 50, illustrated in FIGS. 13 and 14 and set forth in detail hereinbelow, governs shifting of reversing valve 28 at the completion of each stroke of drive piston 30. Once piston 30 has reached the bottom of its stroke, valve 28 is reversed to the position shown in FIG. 12. Then drive fluid is fed from line 26 through valve 28 to line 92 and the bottom of piston 30, while fluid above piston 30 is bled through manifold 96 to line 94, through valve 28, to return line 34.

A second embodiment of the drive cylinder of the invention is illustrated in FIG. 9. A concentric dual drive piston and cylinder arrangement is provided which eliminates the slender rod 60 of the first embodiment, having a relatively low length to radius factor and thus requiring a rather slender drive rod 60 to provide sufficient piston area on top of piston 30 for satisfactory downward drive force.

In the embodiment illustrated in FIG. 9, fluid lines 92, 94, manifold 96 defined by jackets 98, 100, ports 102, chevron seals 104 and packing ring 106, and spacer ring 108 are similar in design and function as in the eembodiment illustrated in FIG. 8. The drive piston is replaced by a movable dual piston and cylinder assembly 112 having a cylinder 114, an upper cap piston 1 l6, driven upwardly by fluid from line 92, and a lower, outer ring piston 118 driven downwardly by fluid from line 94. A fixed tube 120 is mounted concentrically inwardly of the other components and has a stationary sealing ring 122 mounted about its upper periphery.

Thus a dead space 124 is defined between tube and inner manifold jacket 100, which may be provided with a vent 126 to carry any excess fluid escaping into or wiped into space 124 back to fluid storage tank 38 (FIG. 11). Sealing rings 128 are provided on movable ring piston 118 and stationary sealing ring 122.

In this embodiment, components may easily be engineered to provide almost equal fluid requirements per foot of travel in both upstroke and downstroke, a difficult task in the embodiment shown in FIG. 8 due to lost reactive surface area because of the presence of drive rod 60. In the embodiment shown in FIG. 9. by way of example, drive cylinder 114 has an I.D. of 6.75 inches, yielding 35.78 in. of drive surface area beneath cap piston 116. At a pressure of 400 psi, 14,300 pounds of lift is provided, the hydraulic fluid requirement being 1.86 gal. per foot of travel. For the downstroke the ID. of manifold jacket 100 is 9.875 inches which converts to a cross section area of 76,589 in. requiring 4.00 gal. per foot to travel. From this must be subtracted the CD. of cylinder 114, to compute the effective drive surface area on the upper side of ring piston 118, this being 7.50 inches which converts to a cross section area of 44.18 in. requiring 2.30 gal. per foot of travel. The fluid difference then is 4.00 minus 2.30 or 1.70 gal. per foot of travel on the downstroke of the unit. Fluid difference, upstroke to downstroke, becomes 1.86 minus 1.70 or 0.16 gallons; thus fluid required is virtually equalized on both strokes by this unique design.

The internal structure of each outboard cushion cylinder 52 is similar, one being illustrated in FIG. 10. Each cushion rod 64 has an outside diameter smaller than the internal diameter of cylinder 52 to minimize friction and consequent drag between the two components. Stabilizing contact is provided by a pair of spacer guides or rings 130 which may be made of suitable antifriction material such as teflon or brass. Preferably, each rod 64 is hollow to minimize weight and cost of construction. The lower end of rod 64 is closed and provided with a convex abutment plate 132 to cushion contact between rod 64 and a free floating cushion piston 134 therebeneath. A free floating piston 134 arrangement in each cushion cylinder is preferred, for in the event of failure in the cushion hydropneumatic circuit or the drive fluid circuit, cushion rods 64 may move independently of pistons 134 therebeneath without damage to the various components of either the drive fluid circuit or the cushion hydropneumatic circult.

Hydraulic locking of a piston 134 within its cylinder 52 is prevented by stacked rings 136 having an inverted U-shaped bleed cup ring 138 therebehind communicating with a weep hole 140 leading to pressure area 142 beneath piston 134. Thus, any fluid scraped from the interior wall of cylinder 52 will pass between rings 136, forcing the outer wall of cup ring 138 inwardly so that fluid passes to weep hole 140. At the upper ends of each cylinder 52, a circular, flexible dust ring seal 144 prevents debris from entering between rod 64 and the interior wall of cushion cylinder 52 (FIG. 7); a breather pipe or opening 146 (FIG. 6) is provided at the top end of each cylinder 52 adjacent dust ring seal 144 to prevent pneumatic lock within cylinder 52 above uppermost guide 130 (FIG. 10) as rod 64 reciprocates.

Returning now to FIGS. 13 and 14, and further discussion of the drive fluid circuit of the invention, a discussion follows of the control 50 for cyclically reversing valve 28. Control assembly 50 is mounted on platform 10 adjacent reversing valve 28 (FIG. 13) and includes a wheel 148 about which is coiled a spring steel strap 150, having one end secured to wheel 148 and its other end secured at any convenient place on the movable upper portion of the invention, such as a reciprocating cushion rod 64, brace 62 or drive cylinder rod 60 (not shown). As the upper part of the invention reciprocates, strap 150 coils and uncoils on wheel 148, thus rotating wheel 148 through about three revolutions for each stroke of the invention. Wheel 148 is connected through a 3 to 1 reduction box 152 to a control wheel 154, which in turn rotates somewhat less than one-half revolution for each stroke of the invention. Thus, the length of strap 150, diameter of wheel 148 and reduction ratio of box 152 are determined so that control wheel 154 rotates through somewhat less than one-half revolution.

A pair of timing studs 156, 158 are mounted on the outer face-of control wheel 154 with a freely rotating cam 160 located therebetween on the same shaft as control wheel 154. A control cam 162 is pivotally mounted at 164 to the left of cam 160 and wheel 154, in line with cam 160 (FIG. 13). In turn, control cam 162 is fixed to the outer end 166 of the valve rod of a four-way spool valve 168, end 166 being spring or pressure loaded to the right'from unit 170. Spool valve 168 is supplied with fluid under pressure from inlet line 172 and has exhaust line 174 leading back to the source of fluid pressure (not shown). Preferably, this pressure source is independent of the sources of pressure for the drive fluid circuit and the hydropneumatic cushion circuit, these systems also being independent of ,each other. Spool valve 168 has control lines 176, 178 leading to each end of a dual action piston and cylinder assembly 180, the piston rod 182 thereof being connected to control arm 184 of reversing valve 28.

On a downstroke of the unit, strap 150 will coil about and rotate wheel 148 in a counterclockwise direction as viewed in FIG. 14 and indicated by arrow 186. Through box 152, control wheel 154 is rotated in the same direction, at aslower rate, thereby moving timing stud 158 against cam 160, forcing it also to rotate counterclockwise. Eventually cam 160 contacts cam 162, forcing it and spool valve rod end 166 to the left against the urging of unit 170, to reverse the flow in lines 176, 178 and cause rod 182 of control cylinder 180 to shift to the right, or solid line position indicated in FIG. 13. Thus, control arm 184 of reversing valve 28 is also shifted 90 to move the valve to the position schematically illustrated in FIG. 12. Now drive circuit fluid is directed beneath piston from line 92 and an upstroke is initiated.

As the upstroke continues, strap 150 rotates wheel 148 in a clockwise direction (FIG. 14), thereby also rotating control wheel 154 in a clockwise manner through gear reduction box 152. Eventually, timing stud 156 will strike the left side of cam 160, raising it to the position illustrated in FIG. 14, out of contact with cam 162. Through urging from unit 170, spool valve rod end 166 is moved to the right, reversing flow in lines 176, 178 to extend or move rod 182 to the left from control cylinder 180, to the position indicated by dot and dash lines in FIG. 13. Thus, reversing valve control arm 184 is shifted to reverse drive circuit fluid flow by shifting valve 28 to the dispositionillustrated schematically in FIG. 11 and begin a downstroke of the unit. Thus, a full operative cycle has beenset forth.

If desired, a prime mover safety shut-off switch 187 may be located adjacent control wheel 154, in the path of travel of timing studs 156 and 158. In the event of.

piston overtravel in either direction, one timing stud 156, 158 will contact the arm of safety switch 186 to shut down the entire system by stopping prime mover 18.

One embodiment of a reversing valve 28 having a 400 g.p.m. flow capacity of 400 psi is shown in FIGS. 15 through 18. Valve 28 includes valve body 188 with four ports arranged at and a rotary plug 190 having a single, operative plate 192. This construction of plug permits cracking of all four ports during movement of the valve body from one 90 limit position to the other, thus resulting in a smooth transition of fluid flow in reversing, and consequently cushioning the invention as reciprocation is reversed at the end of each stroke.

Reference is now made to FIGS. 18, 19 and 20 for an explanation of the unique hydropneumatic cushion system 48 of the invention. Platform 10 encases two pairs of tanks, these being an outboard bank of two compressed air tanks 194 and an inboard pair of liquid and compressed air tanks 196. All four tanks are manifolded to each other at 198 and supplied with compressed air from air compressor 46 via feed line 200. Lines 202, 202 lead from cushion cylinders 52, 52 to inboard tanks 196, 196 (FIG. 3). At the rear of tanks 196, 196 is a liquid level gauge 204 for visually observing the level of liquid in these tanks. In the embodiment shown in FIG. 3 three air tanks 194, 194, 194 are provided, interspersed with tanks 196, 196.

As illustrated in FIG. 21, each line 202 includes a unique, elongated anti-slosh pipe 206 having a spaced series of downwardly directed slots or openings 208 therein. The cushioning system is entirely closed and each pressure area 142 within cylinder 52, beneath piston 134, line 202 and about half of liquid and compressed air tank 196 are filled with non-emulisfying liquid or hydraulic fluid to prevent mixture of the liquid with compressed air and consequent foaming within the system. The unique anti-slosh pipes 206, 206 assure a steady rise and fall of liquid with each stroke of the pump without any fore to aft or side-to-side sloshing of liquid in the tanks 196, 196.

With each downstroke of the invention, liquid rises within each tank 196 to about a point indicated by line 210 in FIG. 19, oil being forced into the tanks by the downward movement of each cushion cylinder piston 134. Maximum pressure is reached within cushioning system at the bottom of each downstroke which, in one embodiment, is about 135 psi. At the termination of an upstroke, the liquid level falls to about a point indicated by line 212 in FIG. 19 with a consequent pressure fall to about 110 psi. Thus, due to the large volume areas provided by the tanks 194 and 196, variation in pressure is kept to about 25 psi thereby minimizing not only the output requirement of air compressor 46 but also minimizing strain on both air compressor 46 and prime mover 18. Additionally, the cushioning system 48 is entirely separate from the prime drive fluid circuit (FIG. 11) to eliminate complex valving arrangements between systems which are so common in the prior art disclosures hereinbefore discussed.

An explanation follows of three embodiments of the invention having the same structural features but varying stroke distances and lift capacities. Ina small embodiment, platform will have dimensions of 15 by 8 feet, with an overall height (top of sheaves 68) of feet at the bottom of a stroke, and 28 feet at the top of a stroke. Thus, the actual stroke of rods 60, 64, 64 is eight feet with an effective stroke in the rod string of 16 feet due to the 2 to 1 ratio sheave and strap arrangement of the invention. The prime mover is a 20 horsepower diesel engine and the pump has a capacity of up to eight strokes or cycles per minute. Peak polish rod load is about 18,000 pounds.

In a slightly larger unit, platform dimensions are 8 feet by 20 feet, with a height of 24 feet, downstroke limit, to 36 feet, upstroke limit. Thus the pump rods have an actual stroke of 12 feet with an effective stroke in the rod string of 24 feet. The prime mover is a 40 horsepower diesel engine and pump capacity is six strokes or cycles per minute. Peak polish rod load is about 25,000 pounds.

A large unit will have platform dimensions of 8 feet by 24 feet and a height of from feet to 46 feet. Thus, pump rod stroke is 16 feet with an effective stroke in the rod string of 32 feet. The prime mover is a 60 horsepower diesel engine, pump capacity being four strokes or cycles per minute, with a peak polish rod load of up to 35,000 pounds.

Obviously then, the present invention provides a remarkably small long stroke oil well pump assembly having extremely high lift capacity for its rather small size. In each of the embodiments described, cushioning assembly 48 is provided with sufficient pressure to lift the weight of the rod string plus one-half of the load of oil being pumped. Thus, on an upstroke, prime mover 18 and pump 24 provide enough force to lift the remaining half of the oil load. On a downstroke, force from pump 24 is provided to work against the continued upward force in the cushioning system 48. The upward force in the cushioning system will be only one-half the oil load, since the rodstring is falling. Thus, force required from the prime mover will again be one-half the oil load; thus drive force required of the prime mover 18 and pump 24 is substantially equalized between upstroke and downstroke. Furthermore, since prior art heavy weight boxes are eliminated, small pressure variations in the cushioning or counterbalancing system 48 may be regulated by suitably controlling the output of air comp'ressor 46, a far safer and simpler procedure.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

l. A well pumping rig comprising: a platform mounting a reciprocable lift device, hydropneumatic pressure counterbalancing means; and pumping means for providing compressed gas for said counterbalancing means; said reciprocable lift device including a centrally disposed vertically reciprocating lift member and lift line means operatively connected to tthe upper end of said reciprocating lift member, said hydropenumatic pressure counterbalancing means comprising a pair of hydraulic fluid filled cushion cylinders arranged adjacent said reciprocating lift member, a cushion piston rod extending upwardly from each of said cushion cylinders and interconnected with said recoprocating lift member upper end, cushion pistons in each cushion cylinder beneath said cushion piston rods, and hydropneumatic tank means mounted in said platform and in fluid communication with said cushion cylinders beneath said cushion pistons, said hydropneumatic tank means comprising surge tank means partially filled with a non-emulsifying hydraulic fluid and partially with said compressed gas, said gas being supplied under pressure from said pumping means, and anti-slosh means in said surge tank means for preventing hydraulic fluid slosh during reciprocation of said reciprocating lift member and said cushion cylinder cushion rods and pistons.

2. The rig as recited in claim 1 wherein said hydropneumatic tank means further comprises second surge tank means filled with compressed gas, manifold means interconnecting said surge tank means partially filled with hydraulic fluid and said second surge tank means, and an inlet line in fluid communication from said manifold to said pumping means for providing compressed gas for said counterbalancing means.

3. The rig as recited in claim 1 wherein each of said anti-slosh means comprises an elongated, relatively narrow diameter tube having spaced openings therealong, and a line communicating said anti-slosh tube to the base of a cushion cylinder.

4. The rig as recited in claim 3 wherein each antislosh tube spaced opening comprises means defining a narrow slot in the bottom of said tube, parallel to the long axis of said anti-slosh tube.

5. The rig as recited in claim 1 wherein each of said cushion cylinders, rods and pistons comprises a vertically disposed cylinder, a hollow, tubular cushion cylinder rod within said vertically disposed cylinder, and a free floating cushion piston, driving its cushion piston rod by abutting the lower end thereof.

6. The rig as recited in claim 5 wherein each cushion piston rod lower end includes an abutment plate having a convex contour arranged to contact said floating piston during upward movement by said floating piston.

7. The rig as recited in claim 5 wherein each cushion cylinder rod has an outside diameter less than the internal diameter of its cylinder, and includes a pair of antifriction guide rings mounted therearound.

8. The rig as recited in claim 7 wherein said guide rings are made of brass.

9. The rig as recited in claim 7 wherein said guide rings are made of a polytetrafluoroethy'lene compound.

10. The rig as recited in claim 7 wherein each cushion cylinder is provided with breather means near the upper end thereof to prevent pneumatic locking of the cushion rod within its cylinder.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 2atent No- 3 777,491 Dated December 11 1973 Inventor-(s) E mil A. Bender It is certified that error appears in-the above-identified patent and that said Letters 'Patent are hereby corrected as shown below:

Column 3, line 13, change "hydarulic" to -hydrauli c-1 Column 4, line 35, change "orimary" to -'p rimary--.

Column 4, line 51, omit "De Laval Turbine, Inc."

Column 4, line 63, insert space between "De Laval" and "Tur".

oiumn 4, line 64, change spelling "IL Tc" to ---Inc-r, Column 5 line 26, cllange "mjaor" to --major--,-. Column 5, line 51, change "loft" to -.--'.'L1'.ft--- "Column 6, line 1, change "srping" to -spring- Column" line 4, change "tine" to -tim e--.

Column 7, line 60, change "eembodiment" to -embodiment-'. column a, line 19, chan e "76,589" to --76.589--'-, 4

Column 9, line 12, insert--gearaft er '3 1:01" and before "reduction" r Column 12, line 10, change "recoprocating" to --reciprocatjing in Signed: and "sealed this 14th day or June 19m; I

(SEAL) Attest:

EDWARD M.FLETCHE:3R,JR. c. MARSIMLLDANN Attes tinc; Officer Commissioner of Patents 

1. A well pumping rig comprising: a platform mounting a reciprocable lift device, hydropneumatic pressure counterbalancing means; and pumping means for providing compressed gas for said counterbalancing means; said reciprocable lift device including a centrally disposed vertically reciprocating lift member and lift line means operatively connected to tthe upper end of said reciprocating lift member, said hydropenumatic pressure counterbalancing means comprising a pair of hydraulic fluid filled cushion cylinders arranged adjacent said reciprocating lift member, a cushion piston rod extending upwardly from each of said cuShion cylinders and interconnected with said recoprocating lift member upper end, cushion pistons in each cushion cylinder beneath said cushion piston rods, and hydropneumatic tank means mounted in said platform and in fluid communication with said cushion cylinders beneath said cushion pistons, said hydropneumatic tank means comprising surge tank means partially filled with a nonemulsifying hydraulic fluid and partially with said compressed gas, said gas being supplied under pressure from said pumping means, and anti-slosh means in said surge tank means for preventing hydraulic fluid slosh during reciprocation of said reciprocating lift member and said cushion cylinder cushion rods and pistons.
 2. The rig as recited in claim 1 wherein said hydro-pneumatic tank means further comprises second surge tank means filled with compressed gas, manifold means interconnecting said surge tank means partially filled with hydraulic fluid and said second surge tank means, and an inlet line in fluid communication from said manifold to said pumping means for providing compressed gas for said counterbalancing means.
 3. The rig as recited in claim 1 wherein each of said anti-slosh means comprises an elongated, relatively narrow diameter tube having spaced openings therealong, and a line communicating said anti-slosh tube to the base of a cushion cylinder.
 4. The rig as recited in claim 3 wherein each anti-slosh tube spaced opening comprises means defining a narrow slot in the bottom of said tube, parallel to the long axis of said anti-slosh tube.
 5. The rig as recited in claim 1 wherein each of said cushion cylinders, rods and pistons comprises a vertically disposed cylinder, a hollow, tubular cushion cylinder rod within said vertically disposed cylinder, and a free floating cushion piston, driving its cushion piston rod by abutting the lower end thereof.
 6. The rig as recited in claim 5 wherein each cushion piston rod lower end includes an abutment plate having a convex contour arranged to contact said floating piston during upward movement by said floating piston.
 7. The rig as recited in claim 5 wherein each cushion cylinder rod has an outside diameter less than the internal diameter of its cylinder, and includes a pair of anti-friction guide rings mounted therearound.
 8. The rig as recited in claim 7 wherein said guide rings are made of brass.
 9. The rig as recited in claim 7 wherein said guide rings are made of a polytetrafluoroethylene compound.
 10. The rig as recited in claim 7 wherein each cushion cylinder is provided with breather means near the upper end thereof to prevent pneumatic locking of the cushion rod within its cylinder. 